Product Key Checker - File Declaring

I am writing a Product key checker for Windows vista and 7, well it works well in both of these operating systems, but the only problem I encounter here is that, I cannot check vista keys when I run this program in 7..and vice versa. I declared the file as seen below.

Declare Auto Function PidGenX Lib "pidgenx.dll" (ByVal one As String, ByVal two As String, ByVal three As String, ByVal four As Integer, ByVal five As IntPtr, ByVal six As IntPtr, ByVal seven As IntPtr) As Integer

The thing I want to know is that how do you declare files, in the same directory as the exe file i.e. the app directory. I wish to have the 'pidgenx.dll' files of both operating systems in folders corresponding to their OS ie vista's pidgenx.dll in folder called Pack\Vista\pidgenx.dll and for 7's as \pack\7\pidgenx.dll